For many Victorians, the idea of the "general extinction" of whole species was one of the most frightening aspects of the theory of evolution. In his poem "In Memoriam" (used frequently in this novel for chapter epigraphs), Tennyson observes that "so careful of the type she [nature] seems, so careless of the single life". Later in the poem he corrects himself:
"'So careful of the type?' but no.
From scarped cliff and quarried stone
She cries, `A thousand types are gone:
I care for nothing, all shall go."